The present invention generally relates to firearms, and more particularly to barrel assemblies for firearms such as rifles and shotguns.
During the discharge of a firearm such as a rifle or shotgun for example, it is advantageous to have the reciprocating bolt locked into the rear of the barrel (i.e. chamber which holds the cartridge or shell) during discharge to prevent combustion gases from escaping and maintaining a closed breech. To ensure a secure lockup and proper positioning of the bolt with respect to the chamber, a parameter referred to as “headspace” is used. This terminology and its meaning are well known in the art. Essentially, headspace is the distance measured from (1) the surface of the barrel associated with the cartridge chamber that engages the cartridge or shell to set its proper insertion depth into the chamber to (2) the front breech face of the bolt that engages the rear end of the chambered cartridge or shell. Because numerous different cartridge or shell designs are available in varying calibers, the points used to measure the headspace parameter will vary depending on the type of ammunition being chambered. As an example, for rimmed cartridges or shells having a rear flange that radially protrudes beyond the outside diameter of the ammunition head, the headspace is generally measured by the axial thickness of the rim. For rimless ammunition, the headspace may be measured between the bolt breech face and the interior chamber surface that engages the shoulder (for tapered cartridges) or front of the ammunition case adjacent the bullet or slug.
In some rimmed ammunition designs, the rearmost annular end of the barrel at the chamber entrance typically defines the rim seat or seating surface that engages the rim of the chambered ammunition and establishes the datum reference line for measuring the headspace. After repeated firing of the firearm over time and loading/unloading cartridges or shells into/from the barrel chamber, this annular seating surface gradually wears especially with auto-loading firearms. This increases the headspace and gap between the rear of the cartridge or shell and the bolt breech face, thereby causing the headspace to eventually become out of “spec” creating an undesirable operating condition. When this occurs, the entire barrel must typically be discarded and replaced in some designs to restore the proper headspace dimension for ensuring that the rear of the cartridge or shell is properly supported during firing to withstand the combustion pressures generated and prevent rupture of the ammunition case.
An improved design is desired.